Pararnavirae

Pararnavirae is a regnum (realm) of viruses within the domain Riboviria. This realm is characterized by viruses that possess a reverse transcription mechanism, which is a hallmark of their replication process. The name "Pararnavirae" is derived from "para," meaning "beside" or "near," and "RNA," indicating their close association with RNA in their replication cycle.

Characteristics

Viruses in the realm Pararnavirae are unique in that they utilize reverse transcriptase, an enzyme that transcribes their RNA genome into DNA. This process is the reverse of the usual transcription process, where DNA is transcribed into RNA. The reverse transcription mechanism allows these viruses to integrate their genetic material into the host's genome, which is a critical step in their replication cycle.

Genome

The genome of Pararnavirae viruses is typically composed of single-stranded RNA (ssRNA) that is reverse-transcribed into double-stranded DNA (dsDNA) during the infection process. This dsDNA is then integrated into the host cell's genome, allowing the virus to hijack the host's cellular machinery for replication and transcription.

Replication Cycle

The replication cycle of Pararnavirae viruses involves several key steps:

1. Entry: The virus enters the host cell through receptor-mediated endocytosis or membrane fusion. 2. Reverse Transcription: Once inside, the viral RNA genome is reverse-transcribed into DNA by the enzyme reverse transcriptase. 3. Integration: The newly synthesized viral DNA is integrated into the host cell's genome by the enzyme integrase. 4. Transcription and Translation: The integrated viral DNA is transcribed into mRNA by the host's RNA polymerase, and the mRNA is translated into viral proteins. 5. Assembly and Release: New viral particles are assembled and released from the host cell to infect new cells.

Taxonomy

The realm Pararnavirae is divided into two subphyla:

• Haploviricotina: This subphylum includes viruses with a simpler genome organization and replication strategy.
• Polyploviricotina: This subphylum includes viruses with more complex genome structures and replication mechanisms.

Significance

Pararnavirae viruses are of significant interest in both medical and evolutionary studies. They include important human pathogens such as the Human Immunodeficiency Virus (HIV), which causes Acquired Immunodeficiency Syndrome (AIDS). Understanding the biology and replication mechanisms of these viruses is crucial for developing antiviral therapies and vaccines.

Also see

• Reverse Transcriptase
• Retrovirus
• Riboviria
• Virus Classification

Virus classification

Diagram of a virus structure